1. Field of the Invention
This invention relates to lightweight head-mounted display systems which can easily be adjusted for viewing imagery within or outside the wearer's primary field of view.
2. Background of the Related Art
Most head-mounted display systems direct the image into the eye with complex optics consisting of lenses, fold mirrors, and/or beamsplitter arrangements. For example, U. S. Pat. Nos. 3,923,370 and 4,761,056 teach of helmet mounted display systems comprising complex optical paths with several reflective optical components to allow the wearer to view a cathode ray tube (CRT). These systems are complex, heavy, expensive, and very restrictive to the wearer. These systems are typically helmet-mounted and are intended for military applications. The system described in U.S. Pat. No. 3,923,370 uses mirrors which need to be carefully mounted to a visor assembly. Also, this patent provides no provision to adjust the imagery out of the wearer's primary field of view. The system described in U.S. Pat. No. 4,761,056 uses a visor which must be integral to its optical system and requires multiple folding mirrors. Hence, the optics cannot be adjusted by a user.
U.S. Pat. Nos. 4,968,123 and 4,153,913 teach of helmet-mounted display systems which project the imagery being viewed into the eyes of the wearer using complex optical paths. The use of a fixed helmet of predefined geometry in the above referenced patents greatly restricts the range of adjustment to the wearer. Often complex relay lenses, fold mirrors, and prisms are used as well, which further complicate the system. In particular, U.S. Pat. No. 4,968,123 employs a complex real optical to direct an image into the wearer's eyes and has no provision to adjust the imagery out of the wearer's primary field of view. U.S. Pat. No. 4,153,913 similarly does not teach any such provision.
Other head-mounted display systems are worn by the user with a headband or similar mounting arrangement. For example, U. S. Pat. No. 5,189,512 teaches of a helmet integrated display where a CRT image is viewed by the wearer in one eye with an occlusion viewed by the other eye. U.S. Pat. No. 5,189,512 teaches a fixed display in front of the eye with the other eye viewing an occluding mask. This cannot provide an unobstructed field of view capability.
U.S. Pat. Nos. 4,869,575 and 5,153,569 teach of smaller head-mounted display systems mounted to the head via eyeglasses or similar arrangements. While these systems offer some degree of adjustment, they do not give the wearer a full range of adjustment capability, and the wearer is restricted to view the display as it is set up. For example, U.S. Pat. No. 4,869,575 teaches an eyeglass mounted display system with no adjustment capability.
Similarly U.S. Pat. No. 5,153,569 teaches a stationary display system with see through or direct viewing capability, but no adjustment to direct the imagery out of the wearer's primary field of view.
U.S. Pat. No. 5,003,300 teaches a head mounted display system which is more light weight and friendly to the wearer, and with some adjustment capability. However, U.S. Pat. No. 5,003,300 does not provide any means of keeping the video imagery within the wearer's eye pupil as the unit is rotated upward or downward only about a rear pivot. In addition, U.S. Pat. No. 5,003,300 teaches only a display with independently illuminated light emitting elements. Also, U.S. Pat. No. 5,003,300 teaches a scanning means of presenting a raster image of the light emitting elements.
Finally, viewing optics in the above systems typically involve the use of two closely spaced cemented doublet achromatic lenses in order to reduce aberrations of imagery. Such lens systems always require at least three different radii of curvature in order to correct the optical aberrations. When air spaced achromatic doublets are used, they almost always use all 4 radii of curvature to reduce the residual aberrations. This large number of radii of curvature results in complicated and expensive imaging optics and hence makes the head-mounted display system more complicated and expensive.